Timing System Project: Cam Timing ???

[d.hitchcock]

My buddy Bob and I dove into the M42 today to replace the timing chain, sprockets, and guides, as well as the water pump, thermostat etc.

This is my first foray into the M42 engine, but I've been up to my elbows in M20 several times, so I was looking forward to this.

I just give a blow-by-blow of how we worked.

Also, I have a question (see below) about cam timing for reassembly, based on what we found when we pulled everything apart.

We removed the hood for ease of access, then dumped the coolant, pulled the radiator, shroud and fan/clutch assembly. A thin 32-mm wrench from a bike shop and a pulley holder make it easy peezee to remove the fan.

The valve cover, cam sensor, and thermostat and housing came off next, followed by the valve cover and front timing cover and the bottom cover. We had to puzzle over the AC compressor for a moment before decoding the method to unbolt it from the bracket, then remove that honking HUGE AC bracket.

Water pump required just a little persuasion to come out.

We were able to break the crank hub bolt with a honkin' big-azz air gun, but we had to open up the regulator and prime the gun with fresh oil.

The timing chain, guides and sprockets all appeared to be in good shape, except we discovered the bottom guide had broken into two pieces. The chain appeared to be the same length as the new chain, so no obvious stretching occurred.

One thing that puzzled us was the cam timing. With the crank locked at TDC, we discovered the cams weren't perfectly timed. The intake cam was just far enough off that we couldn't insert the cam locking tool. The cam was off by less than a degree, but just enough to prevent the cam tool from working.

We wound up loosening the bolts on the intake cam sprocket, which allowed us to tweak the cam position to accomodate the TDC tool.

I assume the TDC lock guarantees proper cam timing for reassembly, correct? Or do we need to worry about readjusting the intake cam back like it was when we opened her up?

Anyway, we had a blast. And thank God all the bolts came out in good shape. Nothing stripped or crossthreaded. I'm anxious to get the car back together tomorrow morning.

We spent about four hours in the shop today, stopping after we installed the new water pump. I had to quit so I could pick my kids up from school and go to work.

We will wrap up tomorrow morning.

Thanks for reading.

d.hitchcock

[bigalrut]

Hey D.,
My son and I did the same thing today and came across the same anomaly you did with the cams being a bit off with the flywheel locked at TDC.  Did you ever get this resolved?  My plan is to rotate the cams so that the cam locking tool fits correctly and then replace timing chain, tensioner and guide rails.  Any help would be appreciated.

[Onz]

That could be due to a previous owner advancing the intake cam 5 deg.  Many m42 drivers modify the intake cam timing to increase the top end a little.